Coated sodium percarbonate particles, process for their preparation, their use and detergent compositions containing them

ABSTRACT

Coated sodium percarbonate particles containing a sodium percarbonate core surrounded by at least one coating layer comprising at least one inorganic coating material, the coated particles having a content of available oxygen of at least 3% by weight, and being fizzy to such an extent that 2 g of the coated particles dissolved in 50 ml of water at 20° C. generate more than 0.4 ml of gas after 2 min. Process for the preparation of such coated sodium percarbonate particles comprising a heat treatment.

The present invention is related to sodium percarbonate particles withfizzing properties (also called effervescent properties).

It is known, as disclosed in the British patent GB 1494543, to treatuncoated sodium percarbonate particles by heating at a temperature of 75to 135° C. for a period of time determined by the temperature, i.e.during 2-6 h at 75° C. and during 5-30 min at 135° C. The so obtainedproduct presents an improved rate of dissolution, so that it can be usedas bleaching agent for clothing for instance, and becomes effervescentHowever, when incorporated into detergent compositions, where it isbrought into contact with substances which enhance the decomposition ofsodium percarbonate, its stability becomes too poor.

The present invention aims to overcome this drawback by providing a newproduct which presents fizzing properties and thus an improved rate ofdissolution when used as bleaching agent in an aqueous medium, and whichis sufficiently stable to be incorporated into detergent compositionswhich contain substances that are detrimental to its stability, such aszeolites.

The invention is therefore related to coated sodium percarbonateparticles containing a sodium percarbonate core surrounded by at leastone coating layer comprising at least one inorganic coating material,the coated particles having a content of available oxygen of at least 3%by weight, and being fizzy to such an extent that 2 g of the coatedparticles dissolved in 50 ml of demineralised water at 20° C. generatemore than 0.4 ml of gas after 2 min.

“Fizzy property” intends to denote the capacity to generate gas, forinstance in the form of visible bubbles, when dissolved in water, thegas escaping from the water. The gas can be mainly oxygen.

One of the essential characteristics of the invention resides in thatthe sodium percarbonate inside the core material, although it issurrounded by a protective coating layer, still presents fizzingproperties. It has indeed been shown surprisingly that the presence of aprotective stabilizing coating layer which has the function ofprotecting the sodium percarbonate core from the outer CONFIRMATION COPYatmosphere and from other surrounding detergent constituents, does notaffect the fining properties of the sodium percarbonate inside the core.

The method used to measure fizzing according to the invention consistsin dissolving 2 g, or 1 g if the product is very fizzy, of the sodiumpercarbonate particles in 50 ml of demineralised water at 20° C. during2 min without stirring. The amount of gas generated during these 2 minis measured by displacement of water in a connected graduated tube.

The coated sodium percarbonate particles of the invention presentgenerally fizzing properties to such an extent that, when dissolving 2g, or 1 g if the product is very fizzy, at least 0.5 ml of gas isgenerated in the method described above, in particular at least 0.6 ml,values of at least 0.7 ml being usual. Sodium percarbonate particleswhich generate in the above method volumes of at least 0.8 ml of gasgive good results, those generating volumes of at least 0.9 ml beingparticularly satisfactory and those generating volumes of at least 1.0ml of gas being especially preferred. The gas volumes generally do notexceed 10 ml, in particular not exceeding 8 ml, and in most cases notexceeding 5 ml.

The coated sodium percarbonate particles of the invention presentusually a content of available oxygen of at least 5% by weight, inparticular at least 7.5% by weight, contents of at least 10% by weightbeing satisfactory and those of at least 11% by weight being possible.The content of available oxygen is generally at most 14% by weight,especially at most 13% by weight. The content of available oxygen ismeasured by titration with potassium permanganate after dissolution insulfuric acid (see ISO standard 1917-1982).

The inorganic coating material present in the coating layer of thecoated sodium percarbonate particles of the invention can contain one ormore materials selected from alkali metal and/or alkaline earth metal(particularly sodium or magnesium) salts of mineral or other inorganicacids and especially sulfate, carbonate, bicarbonate, phosphate and/orpolymeric phosphates, silicates, borates and the corresponding boricacids. Particular combinations of coating agents includecarbonate/sulfate, and boric acid or borate with sulfate and thecombination of a) sulfate, carbonate, carbonate/sulfate, bicarbonate,boric acid, borate, boric acid/sulfate, or borate/sulfate, with b)silicate. Preferably, the inorganic coating material contains sodiumsilicate, sodium borate, boric acid, sodium carbonate, sodium sulfate,magnesium sulfate or one of their mixtures.

The coating layer present in the sodium percarbonate particles of theinvention represents in general from 0.1 to 20% by weight of the coatedsodium percarbonate particles, in particular from 0.5 to 10% by weight,values from 1 to % by weight giving good results.

The coated sodium percarbonate particles of the invention usually have a90% dissolution time of at least 0.5 min, in particular at least 0.9min.

Generally, the 90% is at most 3 min, especially at most 2.5 min. The 90%dissolution time is the time taken for conductivity to achieve 90% ofits final value after addition of the coated sodium percarbonateparticles to water at 15° C. and 2 g/l concentration. The method used isadapted from ISO 3123-1976 for industrial perborates, the onlydifferences being the stirrer height that is 1 mm from the beaker bottomand a 2 liter beaker (internal diameter 120 mm).

The coated sodium percarbonate particles of the invention have generallya mean diameter of at least 400 μm, in particular at least 500 μm. Themean diameter is usually at most 1200 μm, especially at most 900 μm.

The coated sodium percarbonate particles of the invention usually have abulk density of at least 0.8 g/cm³, in particular at least 0.9 g/cm³. Itis generally at most 1.2 g/cm³, especially at most 1.1 g/cm³. The bulkdensity is measured by recording the mass of a sample in a stainlesssteel cylinder of internal height and diameter of 86.1 mm, after runningthe sample out of a funnel (upper internal diameter 108 mm, lowerinternal diameter 40 mm, height 130 mm) placed 50 mm directly above thereceiver.

The coated sodium percarbonate particles of the invention usually havean attrition measured according to the ISO standard method 5937-1980 ofat most 10%, in particular at most 8%, especially at most 4%. Theattrition is in most cases at least 0.05%.

The coated sodium percarbonate particles of the invention usually have athermal stability, measured using microcalorimetry at 40° C., of at most12 μW/g, especially at most 4 μW/g. Values of at most 3 μW/g give goodresults. The thermal stability is in most cases at least 0.1 μW/g. Themeasurement of thermal stability consists of using the heat flow or heatleakage principle using a LKB 2277 Bio Activity Monitor. The heat flowbetween an ampoule containing the coated sodium percarbonate particlesand a temperature controlled water bath is measured and compared to areference material with a known heat of reaction. The coated sodiumpercarbonate particles of the invention present in general a moisturepick-up when measured in a test conducted in a humidity room at 80%relative humidity and 32° C. after 24 hours, which varies from 1 to 50g/1000 g sample. It varies in particular from 5 to 30 g/1000 g sample,and is preferably from 10 to 15 g/1000 g sample. The moisture pick-up ismeasured by the test described in the international application WO97/35951 of SOLVAY XEROX at page 7, line 25-page 8, line 6, the contentof which is incorporated herein by reference.

The coated sodium percarbonate particles of the invention can beobtained by a process comprising a first step in which the sodiumpercarbonate core particles are prepared, at least one subsequentcoating step in which the core particles are coated with the coatingmaterial, and a heat treatment between the first step and the subsequentstep, or during the subsequent step, or after the subsequent step, theheat treatment being carried out by heating the particles up to an endtemperature T and maintaining the particles during a period t at thisend temperature T, T (expressed in ° C.) and t (expressed in min)corresponding to the formulaT≧0.000567t ²−0.24t+114,490 when T is up to 110° C., andT≧−2t+150 when T is above 110° C.

The present invention therefore also concerns a process for thepreparation of the above-described coated sodium percarbonate particles,comprising a first step in which sodium percarbonate core particles areprepared, at least one subsequent coating step in which the coreparticles are coated with the coating material, and a heat treatmentbetween the first step and the subsequent step, or during the subsequentstep, or after the subsequent step, the heat treatment being carried outby heating the particles up to an end temperature T and maintaining theparticles during a period t at this end temperature T, T (expressed in °C.) and t (expressed in min) corresponding to the formulaT≧0.000567t ²−0.24t+114,490 when T is up to 110° C., andT≧−2t+150 when T is above 110° C.

The first step of the process of the invention can be any known processfor the preparation of sodium percarbonate core particles. It can be forinstance a liquid crystallization process such as the one described inthe international application WO 97/35806 of SOLVAY INTEROX, optionallyfollowed by a conventional drying step. It can also be a fluid bedgranulation process. The first step can be carried out by reacting ahydrogen peroxide solution with a sodium carbonate solution.Alternatively, it can also be a direct process by reaction of a hydrogenperoxide solution with solid sodium carbonate and/or bicarbonate.

In the case of a liquid crystallization process followed by a dryingstep, or in the case of a fluid bed granulation process, the sodiumpercarbonate core particles obtained in the first step of the process ofthe invention are dry particles of sodium percarbonate containing ingeneral less than 1.5% by weight of water, in particular less than 1% byweight of water, a water content of at most 0.8% by weight being mostpreferred. In the case of a liquid crystallization-process withoutdrying step, the sodium percarbonate core particles obtained in thefirst step of the process of the invention are wet particles containingcommonly more than 1% by weight of water, the water content beinggenerally up to 15% by weight.

The subsequent coating step of the process of the invention can becarried out by any known coating process, such as by bringing the sodiumpercarbonate core particles in contact with a solution of the coatingmaterial or with a slurry of the coating material or with the coatingmaterial in powder form. Any type of mixing process or fluid bed reactorcan be used for this purpose.

The heat treatment of the process of the invention is the step whichseems to confer the fizzing properties to the sodium percarbonateparticles. It can be carried out before (i.e. between the first step andthe subsequent step), during or after the coating step. It is preferablycarried out after the coating step. When it is carried out in a separateprocess step, it can be done in any reactor, such as in a fluid bedreactor, oven or in a circulating air oven. A fluid bed reactor in whichthe sodium percarbonate particles are fluidized by an upward flow of hotair is preferred.

The heat treatment of the process of the invention consists in heatingup the sodium percarbonate particles up to an end temperature T andmaintaining the particles during a period t at this end temperature T. Tand t respond to the formula given above. T is generally from 80 to 140°C., in particular from 90 to 130° C., temperatures ranging from 100 to120° C. being particularly satisfactory. The period t is commonlyranging from 5 min to 4 h, in particular from 5 min to 1.5 h, periodsranging from 5 min to 60 min being advantageous.

The heat treatment can be carried out at any pressure. Pressures near orequal to atmospheric pressure are preferred.

The heat treatment of the process of the invention is advantageouslyfollowed by a cooling step. This can be done in a fluid bed with coolingair, by contact with cooled plates, by cooling with air in a thin layer,or in a cooled screw conveyor. The sodium percarbonate particles arepreferably cooled to a temperature below 70° C., especially below 30° C.

The sodium percarbonate particles of the invention can advantageously beused as active bleach constituent in detergent compositions.

The present invention therefore concerns also the use of theabove-described sodium percarbonate particles as active bleach indetergent compositions.

The present invention also concerns detergent compositions containingthe above-described sodium percarbonate particles as active bleachconstituent. The detergent compositions can also contain a builder,either zeolitic or non-zeolitic. The detergent compositions can alsocontain other constituents such as surfactants, anti-redeposition andsoil suspension agents, bleach activators, optical brightening agents,soil release agents, sud controllers, enzymes, fabric softening agents,perfumes, colours and processing aids.

The detergent compositions can take any form such as powders, tablets,liquids, etc.

EXAMPLES

Commercial coated sodium percarbonate particles of SOLVAY with aninitial content of available oxygen of 13.96% by weight have been heattreated in a fluid bed with constant air supply at differenttemperatures. The time and temperature of the heat treatments are givenin the table below. 500 g of coated sodium percarbonate particles wereused per test. The thus treated particles were then cooled down toambient temperature. The so obtained particles were analyzed in order tomeasure their final content of available oxygen and their fizzynessaccording to the method described above by dissolving 1 g. The resultsare given in the table below. Temperature Time t of the T of the heatFinal content of heat treatment treatment available oxygen FizzynessExample (min) (° C.) (% wt) (ml) 1 240   90 13.69 0.5 2 150  100 13.491.1 3 60 110 12.99 2.0 4 45 120 12.39 3.2 5 30 130 9.75 5.8 6 15 1409.69 6.15

1-11. (canceled)
 12. Coated sodium percarbonate particles comprising asodium percarbonate core surrounded by at least one coating layercomprising at least one inorganic coating material, the coated particleshaving a content of available oxygen of at least 3% by weight, and beingfizzy to such an extent that 2 g of the coated particles dissolved in 50ml of water at 20° C. generate more than 0.4 ml of gas after 2 min. 13.The coated sodium percarbonate particles according to claim 12, beingfizzy to such an extent that 2 g of the coated particles dissolved in 50ml of water at 20° C. generate at least 1 ml of gas after 2 min.
 14. Thecoated sodium percarbonate particles according to claim 12, being fizzyto such an extent that 1 g of the coated particles dissolved in 50 ml ofwater at 20° C. generates at least 0.4 ml of gas after 2 min.
 15. Thecoated sodium percarbonate particles according to claim 12, having acontent of available oxygen of at least 10% by weight.
 16. The coatedsodium percarbonate particles according to claim 12, wherein theinorganic coating material is selected from the group consisting ofsodium silicate, sodium borate, boric acid, sodium carbonate, sodiumsulfate, magnesium sulfate and mixtures thereof.
 17. A process for thepreparation of the coated sodium percarbonate particles of claim 12,comprising a first step in which the sodium percarbonate core particlesare prepared, at least one subsequent coating step in which the coreparticles are coated with the coating material, and a heat treatmentcarried out between the first step and the subsequent step, or duringthe subsequent step, or after the subsequent step, the heat treatmentbeing carried out by heating the particles up to an end temperature Tand maintaining the particles during a period t at the end temperatureT, T (expressed in ° C.) and t (expressed in min) corresponding to theformula:T≧0.000567t ²−0.24t+114.490 when T is up to 110° C., andT≧−2t+150 when T is above 110° C.
 18. The process according to claim 17,in which the end temperature T of the heat treatment ranges from 80 to140° C.
 19. The process according to claim 17, in which the period t ofthe heat treatment ranges from 5 min to 4 h.
 20. The process accordingto claim 17, wherein the heat treatment is carried out in a fluid bedreactor in which the particles are fluidized by an upward flow of hotair.
 21. A process of preparing a detergent composition with activebleach, comprising adding the coated sodium percarbonate particles ofclaim 12, as active bleach constituent, in a detergent composition. 22.Detergent compositions comprising the coated sodium percarbonateparticles of claim 12 as active bleach constituent.